Most people build Lotus Seven Inspired Sportscars (LSIS) with the seat fixed against the rear bulkhead. I am short. My wife is shorter. If I want both of us to be able to drive the car, I need an adjustable seat. If I ever want to be able to sell the car I need the seat to be able to move back from where I will normally have it since 97% of all male adults are taller than I am. So that sets the constraints.
Sam Buchanan has a nice design for a seat adjustment bracket but I had an additional problem that made that idea impractical. Did I mention that my wife and I are short? Sitting with the seat on the floor of the car I could barely see over the bonnet bulge. I was much more comfortable with the seat raised a bit. Since this car will in all likelihood never see a race I don’t need to be overly concerned about raising the CG (and my driving skills are such that a slightly higher CG wouldn’t be noticed!). So I need to lift the seat, and make it adjustable, so I need a slider. After searching for a while I came across a set of sliders designed for off road carts. The key to these is that they do not have cross pieces built inso can be customized to whatever width you need.
I mounted these in the car so that when they were furthest back they just touched the read bulkhead. Then I welded some aluminum brackets out of aluminum angle to mount the seat to the sliders. With all four bolts holding the seat down there is very little flex in the stock fiberglass seat. There is seven inches of adjustment and the position I find the most comfortable is just about in the middle of the range. The seat is about 1.5 inches higher than with the seat on the bottom.